V. I. Davydenko

Advances in neutral-beam-based diagnostics on the Madison Symmetric Torus reversed-field pinch (invited)

Innovative charge-exchange recombination spectroscopy (CHERS), motional Stark effect (MSE), and Rutherford scattering diagnostics are now in operation on the Madison Symmetric Torus (MST) reversed-field pinch (RFP). The CHERS diagnostic measures impurity ion flow and temperature, localized to 2cm with high time resolution (∼100kHz). A spectral MSE diagnostic has been in use for five years, measuring ∣B∣ down to 0.2T with high precision (∼2%) and good time resolution (10kHz). The Rutherford scattering diagnostic has demonstrated the robustness of this technique for reliable measurement of majority (D) ion temperature, also with high time resolution. MST is a large RFP (R=1.5m, a=0.52m) operated at moderate current (Ip⩽600kA), with ne typically (1–2)×1019m−3 and Te, Ti⩽2keV. Two compact and reliable diagnostic neutral beams are installed on MST. These beams are short pulse, intense, monoenergetic, and low divergence. The first, a neutral H beam, is used in combination with ultraviolet and visible spectrosco...

Radio frequency ion source for plasma diagnostics in magnetic fusion experiments

Low-divergent quasistationary neutral beams are often applied in modern magnetic fusion devices as a diagnostic tool providing unique information about plasma parameters. The most important requirements of these beams are sufficiently large current and energy of the particles, so that the beam can penetrate to the plasma core. Also the duration of the beams must be long enough, i.e., close to that of a plasma discharge, amounting to at least a few seconds for large fusion devices. We developed a neutral beam injector for plasma diagnostics in the tokamak TEXTOR-94 which is capable of meeting these requirements. The maximum beam energy is 50 keV and the source operated in hydrogen delivers an ion current of up to 2 A with a pulse duration of up to 4 s. The low divergent beam (∼0.5°– 0.6°) is geometrically focused 4 m downstream from the source having a 1/e width of ∼ 70 mm at the focal point. The beam can be modulated with a frequency variable up to 500 Hz. The ion source plasma is produced by a radio freq...

First charge exchange recombination spectroscopy and motional Stark effect results from the Madison Symmetric Torus reversed field pinch

We report on the first results of charge exchange recombination spectroscopy (CHERS) and motional Stark effect (MSE) measurements in the Madison Symmetric Torus reversed field pinch. A 30 keV, 4 A neutral H beam is used in combination with visible and ultraviolet spectroscopy to make the measurements. For CHERS, we find that the C VI line at 3433.69 A yields the largest charge-exchange signal/background ratio and is most clearly resolved from other nearby lines. Equilibrium ion temperature measurements have been made with an existing fast Doppler spectrometer and a higher throughput spectrometer is being designed to do velocity and temperature fluctuation measurements. MSE measurements are made by recording the Doppler shifted Hα spectrum emitted by the beam with a charge coupled device and imaging spectrometer. We have observed separation of the π components of the Stark manifold at magnetic fields of about 0.5 T and are considering options for increasing measurement accuracy.

Ion sources at the Novosibirsk Institute of Nuclear Physics (invited)

A review of investigations in the physics and technology of ion sources, developed in the Institute of Nuclear Physics in Novosibirsk is presented. Distinctive features of physical processes and technical characteristics of plasma sources of gaseous ions, negative ion surface‐plasma sources, electrohydrodynamic (liquid metal) ion sources are considered. In original design plasma sources, ion beams with a current of up to 90 A and energies 1–30 keV are formed by four‐electrode multislit extraction systems from highly ionized, high brightness plasma flux, generated by an high‐current arc discharge with a cold cathode in a small cross‐section diaphragmed channel, and directed with a magnetic field of a special configuration. Plasma jet expansion for a very low ion temperature (0.1 eV) production is used. In surface plasma sources, the fluxes of negative ions are produced when electrons are captured from the electrode surface at the electron affinity level of sputtered and reflected particles. A discharge of ...

A diagnostic neutral beam system for the MST reversed-field pinch

A diagnostic neutral beam system has been developed for the Madison symmetric torus (MST) reversed-field pinch. The system is primarily used: (1) for measurement of the majority ion equilibrium and fluctuating velocity and temperature by Rutherford scattering (RS); (2) for measurement of the impurity ion velocity and temperature, both equilibrium and fluctuating, by charge-exchange recombination spectroscopy (CHERS); and (3) for magnetic field measurement via motional Stark effect (MSE). The system consists of two neutral beam injectors, and two neutral particle analyzers. One injector creates a 20 keV, 4 A helium beam for RS. The energy spectra of the helium beam atoms scattered from the plasma ions is measured with two 12-channel, 45° electrostatic energy analyzers equipped with a hydrogen stripping cell. A second injector creates a 30 keV, 4 A hydrogen beam, which is used for the CHERS and MSE diagnostics. In each injector ions are extracted from a plasma created by an arc discharge source and, after a...

Characterization of 1 MW, 40 keV, 1 s neutral beam for plasma heating

Neutral beam with geometrical focusing for plasma heating in moderate-size plasma devices has been developed in Budker Institute of Nuclear Physics, Novosibirsk. When operated with hydrogen, the neutral beam power is 1 MW, pulse duration is 1 s, beam energy is 40 keV, and angular divergence is 1.2 degrees. Initial ion beam is extracted and accelerated by triode multiapertures ion-optical system. To produce 1 MW neutral beam, about 40 A proton current is extracted with nominal current density of 320 mA/cm(2). Ion-optical system has 200 mm diameter grids with 44% transparency. The grids have inertia cooling and heat is removed between the pulses by water flowing in channels placed on periphery of the grids. A plasma emitter for ion extraction is produced by rf-plasma box. Ion species mix of rf plasma source amounts to 70%, 20%, and 10% of H(+), H(2)(+), and H(3)(+) ions, respectively, by current. Heavy impurities contribute less than 0.3%.

Novosibirsk Project of Gas-Dynamic Multiple-Mirror Trap

Development of a new linear device for confinement of fusion plasmas is under way in the Budker Institute of Nuclear Physics, Novosibirsk. The new device combines features of existing GOL-3 and GDT traps, namely, the central GDT-like cell with sloshing ions produced by intense neutral beam injection, and the multiple-mirror end sections for suppression of axial plasma losses. It is designed as a prototype of an energy-efficient neutron source and a testbed for development of mirror-based fusion reactors.

Rutherford scattering diagnostic for the Madison symmetric torus reversed-field pinch

The technique of Rutherford scattering (RS) has been used (for the first time on a reversed-field pinch) to measure the bulk majority ion temperature on the Madison symmetric torus (MST). RS has been in routine operation on MST since December 1999. The neutral beam source and electrostatic energy analyzers which comprise the RS diagnostic were built by the Budker Institute of Nuclear Physics (Novosibrsk, Russia). The source is described in another paper (Abdrashitov et al., these proceedings) and the analyzers are described. A data analysis routine has been developed which yields accurate fits to the data, and estimates of errors in the fit parameters. Typical results are shown.

Optimization of an ion-optics system with “thick” electrodes for the diagnostic neutral beam injector of the TEXTOR tokamak

The optimization results of the ion-optics system in a neutral beam injector are considered which is developed for application of beam emission spectroscopy in the TEXTOR tokamak. The injector is capable to deliver a neutral beam of at least 1 A in hydrogen and deuterium at 50 keV for a pulse length of 5 s into the plasma. The simulation results with the AXCEL code for grids of 4 mm thickness are discussed. The ion current of 2 A extracted by a multihole grid system at a current density of 120 mA/cm2 is generated by a rf driven ion source. The beamlet half angular divergence is below 0.6° for the optimized four-electrode ion optics system. The estimated temperature rise of the inertially cooled molybdenum grids with 150 holes and 58% transparency is max. 270 K and the related degradation in beam quality by thermal grid expansion is acceptable.

Low energy, high power hydrogen neutral beam for plasma heating

A high power, relatively low energy neutral beam injector was developed to upgrade of the neutral beam system of the gas dynamic trap device and C2-U experiment. The ion source of the injector produces a proton beam with the particle energy of 15 keV, current of up to 175 A, and pulse duration of a few milliseconds. The plasma emitter of the ion source is produced by superimposing highly ionized plasma jets from an array of four arc-discharge plasma generators. A multipole magnetic field produced with permanent magnets at the periphery of the plasma box is used to increase the efficiency and improve the uniformity of the plasma emitter. Multi-slit grids with 48% transparency are fabricated from bronze plates, which are spherically shaped to provide geometrical beam focusing. The focal length of the Ion Optical System (IOS) is 3.5 m and the initial beam diameter is 34 cm. The IOS geometry and grid potentials were optimized numerically to ensure accurate beam formation. The measured angular divergences of the beam are ±0.01 rad parallel to the slits and ±0.03 rad in the transverse direction.